Existing wireless system architectural configurations impose stringent constraints on the system designer with regards to receiving communication signals. Moreover, such configurations often provide low reliability communication links, high operating costs, and an undesirably low level of integration with other system components.
As shown in FIG. 1, a conventional RF receiver 100 includes an analog radio receiver 105, at least one analog to digital converter (ADC) 110, a controller 115 and a modem 120. The analog radio receiver 105 is a direct conversion (DC) receiver which includes an antenna 125 for receiving a wireless communication signal, a bandpass filter 130, a low noise amplifier (LNA) 135, an optional second filter 140 (e.g., bandpass filter), a demodulator 145 having two outputs 150, 155, a phase-locked loop (PLL) 160 and first and second analog low pass filters (LPFs) 165, 170 for controlling bandwidth selectivity.
The modem 120 controls the switching of the LNA 135. The PLL 160 generates a local oscillator (LO) signal to control the two outputs 150, 155 of the demodulator 145. The output 150 is an in-phase (I) output of the demodulator 145 for outputting a real signal component of the wireless communication signal. The output 155 is a quadrature (Q) output of the demodulator 145 for outputting an imaginary signal component of the wireless communication signal.
In the conventional RF receiver 100 of FIG. 1, the ADC 110 is connected to the real and imaginary signal outputs 150, 155, via the analog LPFs 165, 170, respectively. An analog real signal component 175 is output from the LPF 165 to a real input port of the ADC 110 and an analog imaginary signal component 180 is output from LPF 170 to an imaginary input port of the ADC 110. The ADC 110 outputs digital real and imaginary signal outputs 185, 190. The controller 115 maintains control over all of the active components of analog radio receiver 105 and the ADC 110.
In the analog radio receiver 105, the analog LPFs 165, 170, are utilized to guarantee the spectral shape of the wireless communication signal received via the antenna 125 before being sampled at the ADC 110. Typically, the specifications (e.g., error vector magnitude) on the analog LPFs 165, 170, are very stringent such that the implementation requires high order filtering. Implementing high order filter designs for the analog LPFs 165, 170, may be complicated and expensive. Thus, the tolerances on parts for the analog LPFs 165, 170 may lead to unacceptable production yield. Reducing the design complexity of the analog LPFs 165, 170, may be accomplished with a lower order filter design with less stringent specifications. However, using such a filter design in the analog LPFs 165, 170, will result in the occurrence of a group delay variation distortion if no compensation is introduced after the analog LPFs 165, 170.
Because the costs of LPFs that process RF analog signals are higher than the components that use DSP, it is desired to provide a digital baseband (DBB) system, including a low cost receiver with low noise and minimal power requirements, which utilizes DSP techniques to compensate for group delay variation distortion caused by analog LPFs.